Method and apparatus for minimizing time of reception during paging

ABSTRACT

A method and apparatus for detecting a periodic message in a mobile communication system includes initiating, at a receiver, a reception of synchronization data a predetermined amount of time prior to a current periodic message. The predetermined amount of time is based on at least one of an estimated signal quality value from at least one prior periodic message and an estimated error in the at least one prior periodic message. The synchronization data is used to achieve synchronization, and the current periodic message is detected based on the synchronization.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates in general to the synchronizationof a receiver with a transmitter in a cellular radio communicationssystem, and in particular to improving stand-by time of a mobileterminal by minimizing the time of reception during paging.

[0003] 2. Description of Related Art

[0004] Code Division Multiple Access (CDMA) systems were developed toallow multiple users to share scarce radio communication resources. InCDMA systems, a number of users are allocated to the same frequency. Todistinguish among signals for different users, each user is assigned apseudo-noise spreading sequence, which a transmitter uses to spread anarrow-band information to a wide-band signal. To detect a CDMA signal,a conventional receiver despreads the received signal using the samespreading sequence that was used by the transmitter.

[0005] WCDMA is an improvement of the CDMA method and has been developedby various organizations around the world. Some of the benefits providedby WCDMA include support for increased bandwidth and bitrates, andprovisions for improved packet data communications and other services.

[0006] An important consideration for mobile terminals in acommunications system is that of stand-by time. Stand-by time of amobile terminal represents the maximum battery life of a mobile terminalwhen not in use for a conversation. To increase the stand-by time of amobile terminal, the power consumption when the mobile terminal isturned on but not in use should be minimized. Power consumption can beminimized by powering off different components in the mobile terminal,such as signal processing circuitry, when the mobile terminal is not inuse. When the mobile terminal is idle, its main task is to monitor apaging data channel and respond to any pages received. The base stationutilizes the paging channel to send out paging messages or notificationsof incoming calls to the mobile terminals. To minimize the time themobile terminal requires to demodulate the paging data channel, anadditional channel denoted as the paging indicator channel istransmitted. The mobile terminal is required to monitor the pagingindicator channel periodically to demodulate the paging indicator.During those periods when the mobile terminal is not required to monitorthe paging indicator channel, the mobile terminal typically conservespower by powering off its receiver.

[0007] In WCDMA systems, synchronization of a mobile terminal with thebase station is done using a common pilot channel, which transmits knownpilot symbols in parallel to a paging indicator channel and a pagingdata channel. These various channels are separated by differentorthogonal codes. To monitor the paging indicator channel, the mobileterminal must first synchronize its receiver with the base stationthrough a process of carrier frequency correction and detection of thechannel impulse response, or path profile. By powering up the receiver,de-spreading the received signal using a common pilot code, and using apath searcher, the mobile terminal can perform carrier frequencycorrection and identify the relevant radio paths. If the synchronizationprocess including the path search is too short, the receiver will not beadequately synchronized with the base station, which can result inerrors in detecting the paging indicator. On the other hand, by using alonger path search, a more accurate radio path estimate and thus bettersynchronization can be achieved. However, any excess time used duringthe path search implies that the mobile terminal has to be turned on fora longer period of time before the actual paging message is received,thereby reducing the stand-by time of the mobile terminal.

[0008] There is a need, therefore, for a method of minimizing the timeof reception during paging when the mobile terminal is communicating ina paging mode while, at the same time, providing for sufficientsynchronization to minimize errors in the detection of pages.

SUMMARY OF THE INVENTION

[0009] The present invention comprises a method and apparatus forreducing time of reception during paging in a cellular communicationsystem.

[0010] In accordance with one embodiment of the invention, there isprovided a method in which a plurality of paging messages are receivedby a receiver. An estimated signal quality value is determined from atleast one of the plurality of paging messages received prior to acurrent paging message. The estimated signal quality value is utilizedto determine a time period for receiving synchronization data and thereceiver is activated during the time period for receivingsynchronization data.

[0011] In accordance with another embodiment of the invention, reducingtime of reception during paging is implemented in an apparatus thatincludes a receiver for receiving a plurality of paging messages. Theapparatus includes a device for determining an estimated signal qualityvalue from at least one of the plurality of paging messages receivedprior to a current paging message and a controller for determining atime period for receiving synchronization data based on the estimatedsignal quality value and for activating the receiver during thedetermined time period to receive the synchronization data. Preferably,the estimated signal quality value relates to an estimatedsignal-to-noise ratio (SNR) or a radio path profile estimate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention,reference is made to the following detailed description taken inconjunction with the accompanying drawings wherein:

[0013]FIG. 1 is a block diagram of a conventional wireless WCDMAcommunication system, in which the present invention can be implemented;

[0014]FIG. 2 illustrates conventional frame structures for communicationchannels in WCDMA communication system;

[0015]FIG. 3 is a flow diagram of a conventional procedure for receivingdata by a mobile terminal while operating in paging mode;

[0016]FIG. 4 is a diagram illustrating frame and slot structures ofvarious communication channels in a WCDMA system along with thecorresponding timing sequence for detection and synchronization of apaging signal in accordance with an embodiment of the present invention;

[0017]FIG. 5 is a flow diagram of a method for reducing time ofreception during paging in accordance with principles of the presentinvention; and

[0018]FIG. 6 is a block diagram of an apparatus for minimizing the timeof reception of a WCDMA receiver in a mobile terminal during paging modein accordance with an embodiment of the present invention.

[0019]FIG. 7 is a block diagram of an apparatus for minimizing the timeof reception of a WCDMA receiver in a mobile terminal during paging modein accordance with another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Reference is now made to the Drawings wherein like referencecharacters denote like or similar parts throughout the various figures.In a preferred embodiment, the present invention is implemented in aWCDMA system. Accordingly, the following description and examples focusprimarily on the use of the invention in connection with a WCDMA system.As will be appreciated by persons of ordinary skill in the art, however,the invention can be used in other wireless communication systems havinga paging indicator channel and a paging message channel with a separatepilot channel, such as CDMA and TDMA.

[0021] Referring now to FIG. 1, there is illustrated a block diagram ofa conventional wireless WCDMA communication system 100, in which thepresent invention can be implemented. User equipment (UE) 105, e.g., amobile terminal, communicates with one or more base stations (BS) 120 aand 120 b. Each base station 120 a and 120 b serves a service areareferred to as a cell. Communication from base stations 120 a and 120 bto the mobile terminal 105 is referred to as a downlink 115 a and 115 b,while communication from the mobile terminal 105 to the base stations120 a and 120 b is referred to as an uplink 110 a and 110 b. Each basestation 120 a and 120 b is connected via an interface 125 a and 125 b toa radio network controller (RNC) 130, which controls the functions ofthe base stations 120 a and 120 b. In addition, the radio networkcontroller 130 is connected to a core network (CN) 140 using aninterface 135. The core network 140 may provide a connection to othernetworks 150, such as public switched telephone networks (PSTN) or basestations of other wireless technologies, such as CDMA or TDMA.

[0022] To increase the stand-by time of a mobile terminal 105, areceiver of the mobile terminal 105, is deactivated when the mobileterminal 105 is not involved in a voice or data call connection. Bypowering off the receiver and other signal processing blocks to minimizecurrent consumption, the stand-by time of the mobile terminal 105 can beincreased. However, the mobile terminal 105 periodically monitors forpage messages sent by the system on the paging channels. Such pagemessages are used to notify the mobile terminal 105 of any incomingcalls. When the mobile terminal 105 receives a paging message indicatingthat the mobile terminal 105 is being paged, the mobile terminal 105begins receiving control data from the radio network controller 130 viaa base station 120. The mobile terminal 105 uses such control data forsetting up a call connection.

[0023] Referring now to FIG. 2, conventional frame and slot structuresof communication channels in a WCDMA system used to monitor for pagingsignal are illustrated. Each slot 201 of a synchronization channel 205includes a sequence of known pilot symbols 203 that convey timing andsystem configuration information to mobile terminals 105 in the cellserved by the base station 120. System acquisition by the mobileterminal 105 begins by locating the synchronization channel 205, whichpermits the mobile terminal 105 to synchronize with the base station 120through a process of path searching, carrier frequency correction, andchannel estimation. Thus, by de-spreading a signal using known pilotsymbols, and using a path searcher, the mobile terminal 105 can performcarrier frequency correction and identify the relevant radio paths.

[0024] In addition, a paging indicator channel 215, which is alsosubdivided into slots 211, transmits paging indicator messages to themobile terminals 105 currently located in the cell. Each mobile terminal105 is assigned a specific, recurring time period 213 in which themobile terminal 105 listens for paging indicator messages. The assignedtime period 213 for the mobile terminal 105 can be identified based oninformation previously received by the mobile terminal 105 on abroadcast channel (not shown) associated with the base station 120.Generally, each such time period 213 is assigned to a group of mobileterminals 105, and thus more than one mobile terminal 105 is listeningfor a paging indicator message at the same time.

[0025] Furthermore, a paging data channel (PDC) 220 includes slots 221that transmit paging data messages 223. Generally, once a mobileterminal 105 detects a page based on a received paging indicatormessage, the mobile terminal 105 further receives an associated pagingdata message 223. The paging data message 223 allows the mobile terminal105 to determine whether it actually has been paged or another mobileterminal from the paging group has been paged or, alternatively, whetherthere was an error in the detection of the paging indicator message.Assuming the mobile terminal 105 has been paged, the paging data message223 contains control information for setting up a call connection. Thesynchronization channel 205, the paging indicator channel 215, and thepaging data channel 220 share the same frequency bandwidth but areseparated by different orthogonal codes.

[0026] Referring now to FIG. 3, there is shown a flow diagram of aconventional procedure 300 for receiving data by a mobile terminal 105while operating in paging mode. In step 305, the mobile terminal 105powers up its receiver and uses the synchronization channel to acquiresynchronization with a base station transmitter. In step 310, the mobileterminal 105 receives a paging indicator message 213 on the pagingindicator channel. The paging indicator channel transmits informationindicating whether there is an incoming call for the mobile terminal105. At step 315, the mobile terminal 105 uses the paging indicator todetermine if a call is intended for the mobile terminal 105. If it isdetermined that a call is intended for the mobile terminal 105, themobile terminal 105 starts to receive, on the paging data channel,control data needed to set up a connection at step 320. However, if thepaging indicator message indicates that there is not an incoming callfor the mobile terminal 105, the receiver within the mobile terminal 105is turned off at step 325, and the mobile terminal 105 waits for thenext paging indicator. As discussed above, the conventional procedurefor receiving paging data by a mobile terminal 105 while operating inthe paging mode requires a path search along with other synchronizationoperations. The longer the path search, the better the synchronization.However, a longer path search causes the receiver of the mobile terminal105 to be turned on for a longer time before the actual paging messageis received, thereby degrading the stand-by performance of the mobileterminal 105.

[0027] In accordance with the principles of the present invention, thestand-by time of a mobile terminal 105 can be improved by minimizing thetime of reception while the mobile terminal 105 is communicating in apaging mode. Initially, it is noted that the time actually required toperform the path search in connection with synchronizing with the basestation 120 is heavily dependent on the current signal-to-noise ratio.By utilizing an estimated signal-to-noise ratio, (SNR), or measure ofsignal strength relative to background noise, from at least one of aplurality of earlier paging messages, it is possible to predictapproximately how much time is required to achieve synchronization. Ifthe SNR of a particular signal is high, the time required forsynchronization of a mobile terminal 105 with the base station 120 isshort. However, if the SNR of a particular signal is low, communicationis generally not as reliable unless steps are taken to increase thesignal level or decrease the noise level. Hence, a longer time intervalis required to achieve synchronization between the mobile terminal 105and the base station 120. Thus, by utilizing the estimatedsignal-to-noise (SNR) as measured during at least one of the earlierpaging messages, the stand-by time of a mobile terminal 105 can beprolonged by adjusting the amount of time the receiver is turned on inaccordance with the estimated SNR.

[0028] In another embodiment of the present invention, the stand-by timeof a mobile terminal 105 can be improved by utilizing informationrelated to the path profile of the radio channel. As known in the art,radio channels are severely impacted by the presence of multipathpropagation. In multipath propagation, the propagating signal isreflected from a number of objects in the physical environment, and thevarious multipath components from the different radio paths arrive at areceiving device at slightly different times due to the time delaysassociated with the multipath propagation. Generally, the differencebetween the shortest and longest time delays of the radio pathsrepresents a delay spread. If the channel has a relatively small numberof radio paths and a low delay spread associated therewith, the timeinterval needed to achieve synchronization between the mobile terminal105 and the base station 120 is short. However, if the channel has arelatively higher number of radio paths and a larger delay spread, thetime interval needed to achieve synchronization between the mobileterminal 105 and the base station 120 is longer. This informationrelated to the number of radio paths and the size of the delay spreadcan be used to predict approximately how much time is required toachieve synchronization. Thus, by utilizing the path profile estimatesdetermined during at least one of the earlier paging messages, thestandby time of a mobile terminal 105 can be prolonged by adjusting theamount of time the receiver is turned on in accordance with theestimated path profiles.

[0029] Referring now to FIG. 4, there is shown a diagram illustratingframe and slot structures of various communication channels in a WCDMAsystem along with the corresponding timing sequence for detection andsynchronization of a paging signal in accordance with an embodiment ofthe present invention. In general, the frame and slot structures of thesynchronization channel 205, the paging indicator channel 215, and thepaging data channel 220 are identical to those shown and described inconnection with FIG. 2. Pursuant to the present invention, however, thetiming of receiver activation and detection is adjusted relative toinformation transmitted on the synchronization channel 205, pagingindicator channel 215, and paging data channel 220.

[0030] When operating in paging mode, a paging group time instantτ_(pi), at which the mobile terminal 105 should listen on the pagingindicator channel 215, is known from information previously received ona broadcast channel. Accordingly, based on an internal clock signal, themobile terminal 105 turns on its receiver prior to the beginning of thepaging group time instant τ_(pi). Pursuant to the present invention, theamount of time τ₁ prior to the beginning of the paging group timeinstant τ_(pi) and the amount of time τ₂ subsequent to the paging grouptime instant τ_(pi) during which the receiver is powered up are derivedfrom signal-to-noise ratio estimates from earlier paging messages or, atthe very beginning of the paging procedure, are predetermined based onsome worst case scenario regarding the signal-to-noise ratio. The amountof time τ₁ prior and the amount of time τ₂ subsequent to the paginggroup time instant τp_(pi) during which the receiver is powered up canalso be derived from information related to the path profile estimatesof the radio channel, such as the number of radio paths and the size ofthe delay spread. Thus, the receiver is turned on during a signalreception period 230 starting at τ_(pi)−τ₁ and ending at τ_(pi)+τ₂.

[0031] The mobile terminal 105 processes the signal received during thesignal reception period 230 using the known pilot symbols to achievesynchronization during a first channel synchronization period 235. Inaddition, the received signal that includes the paging indicator isstored during a paging indicator interval 240 that begins at the knownpaging group time instant τ_(pi). The stored signal is then decodedusing the appropriate paging indicator code and in accordance with theidentified path profile and synchronization information to detect thepaging indicator (as indicated at 245).

[0032] If the detected paging indicator indicates that the mobileterminal 105 is being paged, the mobile terminal 105 must again turn onits receiver to listen to a paging data message on the paging datachannel. The paging data time instant τ_(pd), at which the mobileterminal should listen for the paging data message, is known either fromsystem specifications or from the broadcast information in theparticular cell. Here again, the amount of time τ₃ prior to thebeginning of the paging data time instant τ_(pd) at which the receiveris powered up is derived from the signal-to-noise ratio estimates, orfrom the path profile estimates, from earlier paging messages. Duringthis second channel synchronization period 250, which begins atτ_(pd)−τ₃, the mobile terminal 105 refines the radio path profileidentified during the first channel synchronization period 235. In somecases, the value of τ₃ can be zero, meaning that the path profileestimate obtained from the first channel synchronization period 235 isgood enough that further path searching is not needed. Finally, thepaging data is detected (as indicated at 255) beginning at the knownpaging data time instant τ_(pd) and continuing until the paging datamessage 223 is fully received.

[0033] Referring now to FIG. 5, there is illustrated a flow diagram 500of a method for reducing time of reception during paging in accordancewith principles of the present invention. Although the steps of themethod are depicted in a particular sequence, it will be appreciated bypersons of ordinary skill in the art that certain steps of the method donot necessarily follow a strict sequence but can be rearranged and/orperformed simultaneously. Upon entering a new cell or first powering up,the mobile terminal 105 receives broadcast channel data at step 502. Thebroadcast channel data can include information relating to paging, suchas an indication of a recurring time instant τ_(pi) regarding when themobile terminal 105 should listen on the paging indicator channel and anindication of a recurring time instant τ_(pd) regarding when to listenon the paging data channel. Once the necessary broadcast channel data isreceived, the receiver of the mobile terminal 105 is turned off at step504 to conserve power. To determine whether the mobile terminal 105 isbeing paged, the receiver is turned on at step 506 to receive the pagingindicator, which is sent at the paging indicator time instant τ_(pi). Toallow time for the receiver to synchronize with the received signal, thereceiver generally needs to begin receiving signals some length of timeτ₁ prior to τ_(pi). Initially, τ₁ is set to some predetermined valuebased on a worst case scenario regarding the signal-to-noise ratio. Oncethe mobile terminal 105 has received at least one paging message,however, the value of τ₁ is derived from signal-to-noise ratio estimatesfrom earlier paging messages.

[0034] Once the receiver is turned on at step 506, the mobile terminalcan initiate a path search at step 508 to correct the carrier frequencyand estimate the path profile of the radio channel using the pilotsymbols on the synchronization channel.

[0035] To provide as accurate of a path profile estimate as possible,the path search generally continues until after the paging indicator isreceived. During the path search, beginning at the paging indicator timeinstant τ_(pi), the received signal including the paging indicatormessage is stored at step 510. The receiver is turned off and the pathsearch is discontinued in step 512 at some length of time τ₂ after thepaging indicator time instant τ_(pi). As with the value τ₁, the value ofτ₂ is initially predetermined based on some worst case scenario and issubsequently derived from signal-to-noise ratio or path profileestimates from earlier paging messages. Then, at step 514, the pathprofile estimate and the paging indicator channel de-spreading code areused to resolve, de-spread, and downsample to symbol rate the storedsignal.

[0036] At step 516, it is determined from the downsampled signal whetherthe paging indicator is true (i.e., whether the mobile terminal 105 isbeing paged). If not, the signal-to-noise ratio (SNR) is updated at step518 based on data from the path search and/or the process of resolving,de-spreading, and downsampling, and new values of τ₁, τ₂, and τ₃ arecomputed at step 520. On the other hand, if the paging indicator istrue, the receiver must again be turned on to receive additionalinformation relating to the page on the paging data channel.Accordingly, the receiver is turned on at step 522 a length of time τ₃prior to the known paging data time instant τ_(pd) to refine the radiopath profile. The value of τ₃ is derived from signal-to-noise ratioestimates from earlier paging messages.

[0037] Using the received paging data, it is determined if the pagingdata is actually intended for the mobile terminal 105 at step 524. Ifso, a call connection with the appropriate base station is initiated atstep 526. If, on the other hand, the paging data indicates that pagingdata is not intended for the mobile terminal, the receiver is turned offat step 528, and the signal-to-noise ratio is updated at step 518. Inthis case, however, the indication that the paging indicator was true,followed by the indication that the paging data is not intended for themobile terminal 105 implies that the detection of the paging indicatorwas erroneous. This error is used in place of and/or in addition to theupdated signal-to-noise ratio estimates from the path search, theresolving, de-spreading, and downsampling process, and/or an estimate ofchannel characteristics to compute new values of τ₁, τ₂, and τ₃ at step520. Typically, the occurrence of such an error indicates that the timeoffsets τ₁, τ₂, and τ₃ should be increased. Once the new values arecomputed, the process returns to step 506, wherein the mobile terminal105 awaits the next recurring paging indicator time instant τ_(pi).

[0038] Referring now to FIG. 6, there is illustrated an apparatus forminimizing the time of reception of a WCDMA receiver 600 in a mobileterminal 105 during paging mode in accordance with an embodiment of thepresent invention. The receiver 600 is turned off for a period of timewhen the mobile terminal 105 is not engaged in a call connection. Duringpaging mode, the mobile terminal 105 has received information regardingthe paging indicator time instant τ_(pi) and the paging data timeinstant τ_(pd). These time instants τ_(pi) and τ_(pd) along with a clocksignal clk are provided to a logic unit 605 (as indicated at 606). Inaddition, time offsets τ₁, τ₂, and τ₃ that indicate when to start andstop receiving data for performing synchronization are stored in acontrol unit 620 and provided to the logic unit 605 (as indicated at607). As discussed above, these time periods τ₁, τ₂, and τ₃ aregenerally derived from signal-to-noise ratio estimates from earlierpaging messages.

[0039] The logic unit 605 uses the received value τ₁, together withτ_(pi) to enable (as indicated at 604) a front end receiver (FeRx) 610to begin receiving data at time τ_(pi)−τ₁ and to enable (as indicated at612) a path searcher 640 to begin correcting the carrier frequency andestimating the path profile of the radio channel using a signal y_(l)received by the front end receiver 610 via an antenna 602. The pathsearcher 640 may contain one or more correlators which continuouslyscans the time delay for a short period of time while looking for strongsignals. The path searcher 640 provides the path profile estimate to aRake receiver 625 and also generates an estimate (S{circumflex over(N)}R) of the signal-to-noise ratio, which is provided to the controlunit 620. Beginning at the paging indicator time instant τ_(pi), thereceived signal y_(l) including the paging indicator is stored in amemory in the Rake receiver 625. At time τ_(pi)+τ₂, the logic unit 605disables the front end receiver 610 (as indicated at 604) and disablesthe path searcher 640 (as indicated at 640). The Rake receiver 625 usesthe estimated path profile received from the path searcher 640 toresolve, de-spread, and downsample the stored signal.

[0040] As known in the art, the Rake receiver 625 remedies the effect ofmultipath propagation. The output x_(k) from the receiver 625 is thenprovided to a paging indicator (PI) detector 630. The paging indicatordetector determines whether there actually exists a paging signal forthe mobile terminal 105 by determining whether the paging indicator istrue ({circumflex over (P)}I=1) or false ({circumflex over (P)}I=0).

[0041] If the paging indicator detector 630 determines that no pagingsignal exists for the mobile terminal 105, the Rake receiver 625provides a signal-to-noise ratio estimate to the control unit 620, andthe control unit 620 computes new values of τ₁, τ₂, and τ₃ based on theold values and the new signal-to-noise ratio estimates. Thus, the logicunit 605 disables the front end receiver 610 until the nextsynchronization period before the next paging indicator message (i.e.,until the next occurrence of τ_(pi)−τ₁) . However, if the pagingindicator detector 630 determines that there is paging of the mobileterminal 105, the logic unit 605 uses the time offset τ₃, along with thepaging data time instant τ_(pd) to enable both the front end receiver610 and the path searcher 640 for refining of the radio path profile. Asmentioned above, the time offset τ₃ can be zero in cases where theestimated path profile from the synchronization for the paging indicatoris of sufficient quality that further path searching is unnecessary. Attime τ_(pd), the path searcher 640 is disabled, and the Rake receiver625 resolves, despreads, and downsamples the received signal y_(l) togenerate an output x_(k). A paging data detector 635 starts to detectthe paging data from the signal x_(k). If the paging data confirms thatthe mobile terminal 105 is being paged, a call connection is establishedbetween the mobile terminal 105 and the base station 120.

[0042] On the other hand, if the paging data was not intended for themobile terminal 105, i.e., {circumflex over (P)}I≠PI, the front endreceiver 610 is disabled, and the control unit 620 updates the valuesτ₁, τ₂, and τ₃ using the estimated signal-to-noise ratio from the pathsearcher 640, the estimated signal-to-noise ratio from the Rake receiver625, and/or information regarding the erroneous detection of a pagingindicator.

[0043] Referring now to FIG. 7, there is illustrated an apparatus forminimizing the time of reception of a WCDMA receiver 600 in a mobileterminal 105 during paging mode in accordance with another embodiment ofthe present invention. The apparatus operates in a similar manner asdiscussed earlier with respect to FIG. 6. However, in accordance withthis embodiment of the present invention, the time offsets τ₁, τ₂, andτ₃ that indicate when to start and stop receiving data for performingsynchronization are generally derived from path profile estimates of theradio channel determined by the path searcher 640. The path searcher 640provides an estimate of the path profile to a control unit 620. Thecontrol unit 620 then computes values of τ₁, τ₂, and τ₃ based oncharacteristics of the estimated path profile, such as the number ofdetected paths, the delay spread among the various paths, and the like.These time offset values are fed to the logic unit 605, which activatesand deactivates the receiver 610 based on the computed time offsetvalues.

[0044] As will be appreciated by those of ordinary skill in the art, thetime offset values τ₁, τ₂, and τ₃ can also be computed in the controlunit 620 based on a combination of two or more of the estimatedsignal-to-noise ratio from the path searcher 640, the estimatedsignal-to-noise ratio from the Rake receiver 625, information regardingany erroneous detection of a paging indicator, and the characteristicsof the estimated path profile.

[0045] Although a preferred embodiment of the method and apparatus ofthe present invention has been illustrated in the accompanying Drawingsand described in the foregoing Detailed Description, it is understoodthat the invention is not limited to the embodiment disclosed, but iscapable of numerous rearrangements, modifications, and substitutionswithout departing from the spirit of the invention as set forth anddefined by the following claims.

What is claimed is:
 1. A method for reducing time of reception duringpaging in a communication system, comprising the steps of: receiving atleast one paging-related message prior to receiving a currentpaging-related message; determining an estimated signal quality valuebased on said at least one paging-related message; determining a timeperiod for receiving synchronization data based on said estimated signalquality value; activating said receiver during said time period toreceive a signal containing said synchronization data; and synchronizingsaid receiver with the received signal based on said synchronizationdata.
 2. The method of claim 1, wherein said at least one paging-relatedmessage includes a paging indicator message transmitted on a pagingindicator channel.
 3. The method of claim 1, wherein said at least onepaging message includes a paging data message transmitted on a pagingdata channel.
 4. The method of claim 1, wherein said estimated signalquality value comprises an estimate of a signal-to-noise ratio (SNR). 5.The method of claim 1, wherein said estimated signal quality valuecorresponds to a radio path profile estimate.
 6. The method of claim 1,wherein said signal received during said time period further includessaid current paging-related message.
 7. The method of claim 6, whereinsaid time period starts at a start time prior to said paging-relatedmessage.
 8. The method of claim 7, wherein the step of determining saidtime period includes identifying said start time based on said estimatedsignal quality value.
 9. The method according to claim 8, wherein saidtime period ends at an end time subsequent to said paging-relatedmessage, the step of determining said time period including identifyingsaid end time based on said estimated signal quality value.
 10. Themethod of claim 9, wherein said paging-related message comprises apaging indicator message.
 11. The method of claim 1, further comprisingthe steps of: updating said estimated signal quality value based on saidcurrent paging-related message; and determining an updated time periodfor receiving synchronization data based on said updated estimatedsignal quality value.
 12. An apparatus for reducing time of receptionduring paging in a communication system, the apparatus comprising: areceiver for receiving a plurality of paging-related messages; a devicefor determining an estimated signal quality value from at least one ofsaid plurality of paging messages received prior to receiving a currentpaging message; and a controller for determining a time period forreceiving synchronization data based on said estimated signal qualityvalue and for activating said receiver during said time period toreceive said synchronization data.
 13. The apparatus of claim 12,further comprising a path searcher for detecting said synchronizationdata.
 14. The apparatus of claim 12, wherein said estimated signalquality value comprises an estimate of a signal-to-noise ratio (SNR).15. The apparatus of claim 12, wherein said estimated signal qualityvalue corresponds to a radio path profile estimate.
 16. The apparatus ofclaim 13, further comprising a rake receiver for de-spreading saidcurrent paging-related message, wherein said paging-related message isreceived during said time period.
 17. The apparatus of claim 16, whereinsaid device comprises at least one of said path searcher and said rakereceiver.
 18. The apparatus of claim 12, wherein said communicationsystem comprises a WCDMA system.
 19. A method for detecting a periodicmessage in a mobile communication system, comprising the steps of:initiating a reception of synchronization data a predetermined amount oftime prior to a current periodic message, said predetermined amount oftime based on at least one of an estimated signal-to-noise ratio (SNR)from at least one prior periodic message, an estimated error in said atleast one prior periodic message, and an estimated radio path profilefrom at least one prior periodic message; using said synchronizationdata to achieve synchronization; and detecting said current periodicmessage based on said synchronization.
 20. The method of claim 19,wherein said step of using said synchronization data comprises at leastone of correcting a carrier frequency and estimating radio channelcharacteristics.
 21. The method of claim 19, further comprising the stepof stopping the reception of said synchronization data a predeterminedamount of time subsequent to said current periodic message, saidpredetermined amount of time subsequent to said current periodic messagebased on at least one of said estimated SNR from said at least one priorperiodic message, said estimated error in said at least one priorperiodic message, and said estimated radio path profile from said atleast one prior periodic message.
 22. The method of claim 21, whereinsaid current periodic message and said at least one prior periodicmessage comprise paging messages.
 23. The method of claim 22, whereinsaid current paging message comprises a paging indicator message. 24.The method of claim 23, wherein, if said paging indicator messageindicates a page, said method further comprising the steps of:initiating a reception of new synchronization data a predeterminedamount of time prior to a paging data message, said predetermined amountof time prior to said paging data message based on at least one of anestimated signal-to-noise ratio, estimated channel characteristics, anestimated paging detection error, and an estimated radio path profile;refining said synchronization using the received new synchronizationdata; and detecting said paging data message.